The invention relates to a measuring instrument according to the preamble to claim 1, in particular a measuring instrument for measuring sample particles moving in a cuvette, for example for measuring their speed and, derived therefrom, their electrophoretic mobility, zeta potential and Brownian particle size, with a filling device for filling and an emptying device for emptying the cuvette, which are mounted at the ends thereof and with devices for irradiating and for monitoring the particles.
The following describes an example of use of a measuring instrument of this kind, wherein it is expressly stressed that the invention does not refer solely to this example of use.
Colloids, emulsions or solid suspensions and mixtures have to be kept stable and homogeneous for the longest possible time. The formulations for these are becoming increasingly complex as the requirements increase. One of the possible methods for stabilising dispersed materials is to optimise electrostatic repulsion between particles of the same type in order to prevent the coagulation of these particles. Another set of problems of interest in this context relates to the targeted destabilisation, and hence separation, of dispersed materials in order to recover the water from the dispersion for the circuit. A large proportion of the measures for separating dispersed materials also involves particle charging, only in this case the charge is brought to zero if possible. However, in all cases it is necessary to know the charge ratios in order to be able to control them. The zeta potential reflects this charge. This can be measured by using a traditional method: microelectrophoresis.
During electrophoresis, electrically charged particles in a suspension or emulsion in an electrophoresis cell in the form of a cuvette are irradiated by means of a laser and by means of a microscope. The images recorded with the microscope are evaluated in order to determine the speed of the particles. The speed of the particles in the electric field is namely a measure for the electric charge whose potential can be depicted as the zeta potential and measured.
A significant problem with measurements of this kind is the exact positioning of the measuring setup or the parts thereof (laser-microscope-cuvette) relative to each other. It is also necessary for the cuvette to be both easy to fill and to clean.